I Field of the Invention
This invention relates to diamond drag bits for drilling earthen formations having polycrystalline diamond inserts imbedded in the cutting face of the bit.
More particularly, this invention relates to matrix type diamond drag bits fabricated by a powder metallurgy process wherein cutter pockets and relief pockets are formed in a female mold to accept and support cylindrically shaped polycrystalline diamond inserts subsequently brazed in place in the pre-formed pockets.
II. Description of the Prior Art
U.S. Pat. No. 5,056,382 entitled MATRIX DIAMOND DRAG BIT WITH PCD CYLINDRICAL CUTTERS, issued Oct. 15, 1991, is assigned to the same assignee as the present invention.
This provides a milled relief pocket adjacent the cutter pocket that is vectored at a different angle than the angle of the cutters oriented in the face of the matrix bit. The relief pocket provides maximum compression support for the base of the PCD cylindrical cutter and increased cylindrical wall support while relieving the cutter back rake surface.
While the foregoing patent is an important advance in the state of the art it was determined in some drilling circumstances that the wide raised support platform surrounding the diamond cylindrical cutter acted as an insert penetration limiting means, i.e. the insert support platform inhibited penetration of the cutter in the rock formation.